Recently, a MIMO technique using multiple transmit and receive (TX/RX) antennas is attracting much attention as one of techniques to satisfy an increasing demand for high-speed and high-quality data transmission. Since the MIMO technique performs communication using the multiple channels resulting from multiple antennas, it can greatly increase the channel capacity in comparison with the case of using a single antenna. For example, if a transmit (TX) node and a receive (RX) node use an M number of TX antennas and an M number of RX antennas, the channels of the respective antennas are independent of one another, and the bandwidth and the total TX power are fixed, the average channel capacity increases M times in comparison with the case of using a single antenna.
The MIMO technique can be classified into a Single User MIMO (SU-MIMO) technique and a Multiple User MIMO (MU-MIMO) technique. The SU-MIMO technique is used to perform one-to-one communication between a pair of TX/RX nodes by allowing the pair of TX/RX nodes to occupy all of the multiple channels resulting from multiple antennas. The MU-MIMO technique is used to perform one-to-many communication between a TX node and multiple RX nodes by dividing the multiple channels resulting from multiple antennas among the multiple RX nodes. Among the MU-MIMO techniques, a technique using a MIMO broadcast channel is attracting attention as the next-generation wireless communication technology.
The MIMO broadcast channel is used to provide downlink communication from a base station having multiple TX antennas to multiple user terminals having one or more RX antennas. One of the most ideal transmission schemes for the MIMO broadcast channel is a Dirty Paper Coding (DPC) scheme capable of achieving the maximum transmission rate. However, the DPC scheme is very difficult to implement in practice. Therefore, various schemes have been proposed that are close in performance to the DPC scheme and are relatively easy to implement in practice.
A nonlinear beamforming scheme has been proposed that is near in performance to the DPC scheme. However, the nonlinear beamforming scheme is difficult to apply to practical systems because it still has very high complexity. There is therefore a need in the art for a low-complexity linear beamforming scheme to perform efficient downlink communication using the MIMO broadcast channel.